A spin vale type electro-magnetic transformation device includes two ferromagnetic layers, which are a pinned layer and a free layer. In the pinned layer, a magnetization direction is fixed with an anti-ferromagnetic layer. In the free layer, the magnetization direction is changed in accordance with magnetic field. A magnetic sensor having the spin vale type electro-magnetic transformation device is well known. The magnetic sensor includes two spin vale type electro-magnetic transformation devices on a substrate so that two devices provide a half bridge circuit. The half bridge circuit functions as a detection portion of the magnetic field. Thus, temperature dependency in each device is cancelled each other.
However, the anti-ferromagnetic layer and the pinned layer composing the device are integrally formed on the same substrate. Therefore, the magnetization direction in the pinned layer stays constant. The magnetization direction is fixed, i.e., pinned with the anti-ferromagnetic layer. Accordingly, when the magnetic field applied to each device is almost the same, output from the half bridge becomes small. Specifically, when the direction of the magnetic field and the magnitude of magnetic flux in the magnetic field applied to each device are the same between two devices, the bridge output is extremely small.
In view of the above problem, a magnetic sensor is disclosed in U.S. Pat. No. 6,734,671. In this sensor, one of spin valve electro-magnetic transformation devices is covered with a magnetic shield layer. Accordingly, even if the magnetic field applied to each device is almost the same, a bridge output from a half bridge is increased.
However, in the above sensor, since one of the spin valve electro-magnetic transformation devices is covered with the magnetic shield layer, a sensitivity of the one spin valve electro-magnetic transformation device is reduced. Thus, resistance change of each device is not sufficiently retrieved as the bridge output, i.e., the sensor has low sensitivity.